US 4,141,719 A · Tantalum metal powder

Abstract

Improved, high-purity agglomerated tantalum powders having an exceptional combination of a relatively low oxygen content, high green strength when pressed into compacts without using any binders, and, when compacted and sintered as anodes for capacitors have reduced shrinkage of the pressed compacts during sintering, and have high electrical capacitance and breakdown voltage along with low direct current leakage and low dissipation factor. Such powder is produced by milling hydrided high-purity tantalum metal ingots to a powder of specified particle size and size distribution, subjecting the powder to a heat treatment at a temperature T-1 to degas and preagglomerate it, milling and screening the degassed and preagglomerated powder to preferably about -200 mesh size, subjecting the -200 mesh powder to a higher temperature T-2 to reagglomerate it, milling and screening the reagglomerated powder to about -35 mesh, and blending the final powder. The final powder is compacted without a binder and sintered to produce anodes of electrolytic capacitors.

Claims31

Dependent claims

A method of manufacturing an improved, high-purity agglomerated tantalum powder having relatively low oxygen content, good flow characteristics and high green strength in the absence of a binder, relatively low shrinkage during sintering, and high specific capacitance in pressed anodes after sintering, which consists essentially of:

(a) reducing and classifying hydrided high-purity tantalum ingots to a precursor powder having a predetermined particle size and particle size distribution,
(b) subjecting the reduced and classified tantalum hydride powder to a heat treatment at a predetermined temperature under chemical nonreactive conditions to degas it at a lower first temperature, and then to preagglomerate the powder at a higher temperature T-1,
(c) reducing the preagglomerated powder to a mesh size of less than 80 mesh,
(d) heating the less than 80 mesh powder under non-reactive conditions to a temperature T-2, which is higher than T-1, to reagglomerate it,
(e) reducing the reagglomerated powder to an intermediate mesh size larger than the mesh size of the preagglomerated powder, and
(f) blending the reduced intermediate mesh size powder to provide a tantalum powder for pressing into shapes for sintering to form low density anodes.

3 more elements

An agglomerated powder selected from the hydride forming metals of Group IVB of the Periodic Table of the Elements comprising titanium, zirconium, and hafnium, and Group VB comprising tantalum, columbium and vanadium, the agglomerated powder produced by the method consisting essentially of:

(a) subjecting the metal to a hydrogen atmosphere to produce a friable mass,
(b) reducing the hydride mass to produce a hydride powder having an average Fisher sub-sieve particle size of less than 10 microns,
(c) heating the hydride powder in a chemically non-reactive environment to remove the hydrogen,
(d) further heating the degassed powder in a chemically non-reactive environment to a sufficient temperature T-1 and for a sufficient time to produce a porous sintered cake in which at least the finer powder particles are bonded,
(e) reducing the porous sintered cake into aggregates of a size of less than 80 mesh and each comprised of multiple initial particles and having an average particle size substantially larger than the average size of the initial particles of the hydride power produced by step (b),
(f) heating the aggregates of less than 80 mesh in a chemically non-reactive environment to a sufficient temperature T-2 which is higher than T-1 and for a sufficient time to produce a reagglomerated porous cake,
(g) reducing the reagglomerated porous cake produced by step (f) into aggregates of multiple initial particles with such aggregates having an average particle size substantially larger than the average size of the initial particles of the hydride powder produced by step (b) and of the aggregates produced by step (e), and
(h) blending the aggregates produced by step (g) to produce the final powder, said final powder having an average green strength of at least 19.5 pounds on cylindrical parts compacted without any binder to a green density of 7.0 grams per cubic centimeter, weighing 2 grams, having a diameter of 0.261 of an inch, and crushed by applying force on the parts laid sideways.

5 more elements

A high-purity agglomerated tantalum powder for making compacted and sintered anodes having:

(a) an oxygen content of not more than 1518 ppm,
(b) a Scott density in the range of about 50 to 65 g/in.sup.3,
(c) an average Fisher sub-sieve size of 7 to 10 microns,
(d) essentially all of its particles passable through a 35 mesh screen,
(e) not more than about 65% by weight of its particles passable through a 325 mesh screen,
(f) a Hall flow time of less than 60 seconds with the Hall flow cup vibrated at a frequency of 3600 cycles per minute and an amplitude of 0.024 inch,
(g) an average green strength of at least 19.5 pounds on 2-gram, 0.261 inch diameter cylinders compacted without any binder to a green density of 7.0 grams per cubic centimeter and crushed by applying force on the cylinders laid sideways,
(h) a linear shrinkage not greater than 3.9% for anodes pressed without any binder to a green density of 7.2 g/cm.sup.3 and sintered for 30 minutes at 1800.degree. C. and not greater than 7.8% for anodes pressed without any binder to a green density of 7.2 g/cm.sup.3 and sintered for 30 minutes at 2000.degree. C.,
(i) a dissipation factor of about 15 to 22% for anodes pressed without any binder to a green density of 7.2 g/cm.sup.3 and sintered for 30 minutes at 1800.degree. C. and of about 10 to 15% for anodes pressed to a green density of 7.2 g/cm.sup.3 and sintered for 30 minutes at 2000.degree. C., and
(j) a specific capacitance expressed as microfarad-volts per gram (CV/g) of at least 3850 on anodes pressed without any binder to a green density of 7.2 g/cm.sup.3, sintered for 30 minutes at 1800.degree. C., anodized in a solution of 0.01% phosphoric acid at 200 volts and tested in a solution of 10% phosphoric acid and of at least 3000 on anodes pressed without any binder to a green density of 7.2 g/cm.sup.3, sintered for 30 minutes at 2000.degree. C., anodized in a solution of 0.01% phosphoric acid at 270 volts, and tested for specific capacitance in a solution of 10% phosphoric acid.

7 more elements

Dependencies are inferred from the claim text.

Tantalum metal powder

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Tantalum metal powder

Life of this patent

Abstract

Claims31